<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box1{
            width:150px;
            height: 150px;
            background-color: darkred;
        }
        .box2{
            width:150px;
            height: 150px;
            background-color: darkblue;

            /*
            绝对定位脱离了文档流*/
            position: absolute;
            left:50px;
            top:-50px;
        }
        .box3{
            width:150px;
            height: 150px;
            background-color: darkgoldenrod;
        }
    </style>
</head>
<body>
<div class="box1"></div>
<div class="box2"></div>
<div class="box3"></div>

</body>
</html>